In recent years, electronic components have been made more and more compact in accordance with miniaturization of devices, e.g., portable phones and the like on which the electronic components are mounted. Thus, there is a bump forming apparatus for this purpose which forms bumps to electrode portions at each circuit formation part on a semiconductor wafer without separating the circuit formation part from the semiconductor wafer. The bump forming apparatus of this kind includes a carry-in device for taking out a semiconductor wafer before bumps are formed thereto from a first storage container where the semiconductor wafers without bumps are stored, a second storage container for storing wafers with the bumps formed, a bonding stage where wafers without bumps are placed and heated generally to about 250-270° C. so as to join the electrode portions and bumps, a carry-out device for storing the wafers after the bumps are formed thereon into the second storage container, and a transfer device for transferring the wafers from the carry-in device to the bonding stage and from the bonding stage to the carry-out device.
Meanwhile, as a SAW (Surface Acoustic Wave) filter used in the aforementioned portable phones and the like, there are some semiconductor wafers having a substrate of the wafer not formed of silicon as in the prior art but formed of quartz, or a compound semiconductor wafer such as lithium tantalum, lithium niobium, gallium arsenide or the like. Although the compound semiconductor wafer of this type is heated as well to approximately 150° C. at maximum in forming the bumps, it is necessary for the heating and cooling speed of the compound semiconductor wafer to be lowered in comparison with the conventional silicon wafer. Unless the cooling is carried out slowly, the compound semiconductor wafer is accompanied by a pyroelectric effect thereby breaking circuits, or the wafer is thermally deformed to crack in some cases.
As such, a bump forming apparatus for forming bumps to the compound semiconductor wafers needs a different way of temperature control from the control in the conventional bump forming apparatus which forms bumps to silicon wafers.
The present invention has for its object to provide a bump forming apparatus which executes temperature control different from the prior art before and after forming bumps to semiconductor wafers, and a bump formation method carried out by the bump forming apparatus.